Boxer, a staunch liberal, calls climate change the "greatest challenge to hit the planet," battles against offshore drilling, rails about the dangers of nuclear power and has pushed to restrict greenhouse gas emissions that contribute to global warming.

Inhofe proudly calls himself an unabashed conservative who dismisses global warming as a hoax and famously tossed a snowball on the Senate floor to prove his point. "It's very, very cold out," he said last February as he lobbed the ball toward the Senate president, an incident that makes Boxer cringe.

Yet somehow, the two have managed to become friends and political partners, working closely together to find common ground and frequently gushing about the other. Earlier this year, Inhofe and Boxer shepherded a sweeping bill to impose new regulations on tens of thousands of toxic chemicals in everyday products, from household cleaners to clothing and furniture. It was the first update of the law in 40 years.

The unlikely alliance played key roles on a 5-year, $305 billion bill to address the nation's aging and congested transportation systems that President Barack Obama signed into law in December. And last week, the pair secured overwhelming support for a $10 billion water projects bill that includes more than $200 million in emergency funds to address a lead-contaminated water crisis in Flint, Michigan, and other cities.

Rep. Tom Cole, R-Okla., compares Boxer and Inhofe to "an old married couple who've sort of learned to live with each other's idiosyncrasies. They raise their eyebrows, but get past it for the sake of the entire partnership."

The senators have known each other since their days in the House in the 1980s.

"I've worked with Barbara a long time. And we like each other personally," says the 81-year-old Inhofe.

Boxer, 75, says their friendship has its limits, but is real: "One is Venus and one is Mars, let's be clear," she said on the Senate floor.

"People wonder how can we possibly bridge the divide," she mused as the Senate debated the water bill. "And it is a fact that on certain issues we can't. There is a lesson there. ... We have never, ever taken those differences and made them personal. We respect each other and we don't waste a lot of time arguing."

Or as Inhofe put it in an interview, "She has every right to be wrong."

The alliance's success stands in stark contrast to the fierce partisanship that has consumed Capitol Hill and grown increasingly worse as the Nov. 8 election approaches. Republicans and Democrats who once had high hopes for criminal justice reform, for instance, and even the basic business of individual spending bills have accepted the reality that little will be done.

Meantime, Inhofe and Boxer plow ahead - together.

"We both like to finish what we started and get things done," said Inhofe, a former real estate developer and Tulsa mayor who still pilots a small plane.

The pairing "sends an important signal to everybody that you don't have to make differences personal and attack someone personally," the Brooklyn-born Boxer said in an interview.

Boxer, who carved out time in a two-decade-plus Senate career to write politics-and-power novels, said lawmakers "need to, while holding your ground and not compromising your core beliefs, find ways to get things done."

Inhofe's status as the Senate's top climate-change doubter has made him the environmental movement's archenemy, but his fondness for political give-and-take has won him another unlikely Senate ally: Vermont's Bernie Sanders.

Sanders, like Boxer a passionate advocate for action to slow climate change, lost a hotly contested race for the Democratic presidential nomination this year. He shocked many supporters when he announced at a town hall this spring that the Republican he likes the most is Inhofe. The revelation might ruin Inhofe's political career, Sanders joked.

"There'll be a 30-second ad: 'Sanders said he likes this person!'" Sanders said, calling Inhofe "a decent guy" and a friend.

Inhofe returns the compliment and said the men became friends after arguing for hours on the Senate floor over a bill on oil drilling.

"I won. He lost," Inhofe said. But he said Sanders later told him: "This is what we should be doing in the Senate - debating issues."

Boxer, who is retiring after a 34-year congressional career, said colleagues from both parties have noticed her partnership with Inhofe and called it a model.

One of those admirers is Senate Majority Leader Mitch McConnell, a Kentucky Republican not known as overly sentimental. "I hate to see the Boxer-Inhofe team come to an end," he said last week.